This invention relates generally to devices and systems for storing and transferring volatile and/or potentially hazardous fluids, particularly such as aircraft fuel in a fuel delivery system for an aircraft. More specifically, this invention relates to an improved variable volume storage tank or reservoir for storing and dispensing a selected fluid such as aircraft fuel or the like, wherein the storage tank substantially precludes the formation of a residual air space or vapor space within the storage tank as fuel is dispensed therefrom, and further wherein the storage tank is provided with externally mounted fluid level sensor means for monitoring the level or volume of fuel remaining within the tank. The variable volume storage tank may be utilized in a variety of fluid transfer applications, such as transfer of potentially hazardous fluids, or transfer of fluids in an outer space environment.
Modern aircraft are commonly equipped with multiple fuel tanks mounted at different positions along the aircraft fuselage and wings, wherein such multiple fuel tanks are designed to carry a substantial quantity of fuel and thereby provide the aircraft with a significant potential range of flight. The fuel tanks are normally interconnected with each other to accommodate inter-tank fuel transfer and thereby permit substantially uniform or balanced distribution of the fuel load throughout the aircraft, particularly as the fuel is depleted during flight operations by delivery to one or more aircraft engines. Moreover, for relatively short range flights, it is common for the aircraft to take off with only a partial fuel load, sometimes with one or more of the fuel tanks in an empty condition in order to reduce overall aircraft weight and thereby improve fuel efficiency. Internal fuel transfer pumps are commonly mounted within the various fuel tanks and can be operated on the ground or in-flight to transfer fuel from one tank to another, or to empty one or more fuel tanks preparatory to short range flight operations. In addition, aircraft fuel tanks are normally equipped with fuel level sensors mounted inside the various tanks to provide the flight crew with an indication of the remaining fuel volume in each tank.
In recent years, a number of aircraft accidents have been attributed to malfunctions associated with fuel tanks and related systems for delivering fuel to the aircraft engines. More specifically, aircraft fuel tanks are normally provided in a fixed volume configuration for containing a specified maximum quantity of fuel in a substantially filled condition. As the fuel is transferred from a tank in the course of fuel usage or as a result of fuel transfer to another tank, a substantial air or vapor space is created within the tank above any fuel remaining therein. This air or vapor space undesirably provides a site for the formation and accumulation of volatile fuel vapors in a high concentration. This accumulation of fuel in vapor form not only wastes fuel and represents a source of air pollution, but also presents a safety hazard in the presence of air and any source of ignition. One potential ignition source comprises the electrically powered and/or friction generating fuel transfer pumps mounted directly within the aircraft fuel tanks. Another potential ignition source comprises other electrically powered devices such as fuel level sensors mounted directly within the fuel tanks.
The present invention seeks to overcome these problems and disadvantages, by providing an improved fuel storage tank or reservoir of variable volume design to substantially eliminate residual air or vapor space when the tank is in an empty or partially empty condition, and further wherein the fuel level within the storage tank is monitored by an externally mounted fuel sensor. The improved variable volume tank of the present invention can be ganged together in a multiple tank system, in an aircraft or other fluid transfer environment, to provide safe and efficient fluid transfer from one location to another.